Manipulation of plants to alter and/or improve phenotypic characteristics such as productivity or quality requires expression of heterologous genes in plant tissues. Such genetic manipulation relies on the availability of a means to drive and to control gene expression as required. For example, genetic manipulation relies on the availability and use of suitable promoters which are effective in plants and which regulate gene expression so as to give the desired effect(s) in the transgenic plant.
Advanced traits often require the coordinated expression of more than one gene in a transgenic plant. For example, to achieve the production of polyunsaturated fatty acids such as archachidonic acid in a plant requires expression of at least 5 genes. There is also increasing demand of trait stacking which requires the combination of more than one gene in transgenic plants.
The availability of suitable promoters for such coordinated expression is limited. Promoters would often need to have the same tissue and/or developmental specificity and preferably comparable expression strength. One solution has been to use the same promoter for the expression of several genes. Expression constructs comprising more than one expression cassette with tandem or inverted sequence repeats of for example a promoter cause various problems. When located on one vector, handling of the vector in bacteria for cloning, amplification and transformation is difficult due to recombination events which lead to the loss and/or rearrangement of part of the expression construct. Moreover, sequence verification of constructs comprising repeated sequences is difficult and sometimes impossible. A further problem of such expression constructs comprising repeats of the same promoter sequence is that recombination may also occur after introduction into the genome of the target organism such as a plant.
Additionally it is well known that repeated promoter sequences in the genome of organisms such as a plant may induce silencing of expression derived from these promoters, for example by methylation of the promoter or increase of chromatin density at the site of the promoters which makes the promoter inaccessible for transcription factors.
The use of different promoters in expression constructs comprising more than one expression cassette is one possibility to circumvent these problems. Isolation and analysis of promoters is laborious and time consuming. It is unpredictable what expression pattern and expression strength an isolated promoter will have and hence a high number of promoters need to be tested in order to find at least two promoters with comparable expression pattern and optionally comparable expression strength.
There is, therefore, a great need in the art for the availability of new sequences that may be used for expression of selected transgenes in economically important plants. It is thus an objective of the present invention to provide new methods for the production of synthetic promoters with identical and/or overlapping expression pattern or expression specificity and optionally similar expression strength. This objective is solved by the present invention.